Abstract : The use of the Global Positioning System (GPS) as a navigation aid for aircraft attempting to locate a ground based electromagnetic energy emitter is studied. In particular, the satellite geometry which yields minimum errors in the emitter location estimation for four different satellite availability cases is explored. This geometry, in general, is not the same as that which yields minimum aircraft navigation errors. Satellite selection criteria are identified and serve as a basis for selection algorithm development. The research shows that emitter location errors can be significantly reduced by selecting satellites based on the criteria presented in this study. Three satellite performance is found to be nearly as good as that obtained using four satellites and, for the two satellite case, emitter location is still better for some period of time than that obtained using four satellites selected to minimize Geometric Dilution of Precision (GDOP).